The present invention relates to a device for swiveling a vehicle seat in a horizontal plane.
The seat swiveling device for use in a vehicle is disclosed in Japanese Utility Model Application Publication No. 5-56582 and the Japanese Unexamined Patent Application Publication No. 10-109575. The latter shows a mechanism for adjusting the swiveling of the vehicle seat as a seat swiveling device for a vehicle.
Such an adjusting mechanism includes a lower base which is fixed to the floor of a vehicle compartment and has an annular support portion, an upper base which is slidably and pivotably mounted on the annular support portion of the lower base and has at its center an opening for fixing therein a vehicle seat assembly, and a holder which holds the upper base in such a way that the upper base is slidable relative to the annular support portion of the lower base. The holder has a cylindrical portion having formed therethrough plural holes which are arranged circumferentially in the cylindrical portion at a predetermined spaced intervals. A lock plate is pivotably mounted to the upper base by a pivot shaft. The lock plate has plural teeth which are engageable with holes in the holder.
In other words, the lock plate performs the function of making the upper base rotatable relative to the lower base or locked to the lower base so that the upper base is unrotatable relative to the lower base. The lock plate is mounted to the lower base by and pivoted about the pivot shaft which is provided on the lower base and has a circular cross section. For that reason, the lock plate has formed therein a shaft hole of a shape of a perfect circle having substantially the same diameter as the pivot shaft. In such an arrangement of the lock plate, therefore, the teeth are moved along a path of an arc centered on the pivot shaft. The teeth are formed in a direction that is substantially the same as the direction tangential to the above path of an arc, and the distance between the center of the pivot shaft and the lateral sides of the engaging teeth is constant.
According to the relative art, the shaft hole in the lock plate is of a perfect circle whose diameter corresponds to the diameter of the pivot shaft, and the distance between the center of the pivot shaft and the lateral sides of the teeth is constant. Therefore, the teeth tend to be engaged with the hole such that only one lateral side of the teeth contacts with one lateral side of the hole. For engaging the teeth and holes such that lateral sides of the teeth are in contact with the lateral sides of the hole with no gap therebetween, the shape of the hole has to correspond exactly to the shape of the teeth and the teeth and their holes have to be precisely positioned relative to each other. Thus, the teeth and the hole need to be formed with high accuracy and the teeth need to be accurately positioned with respect to the teeth in turning the vehicle seat assembly. In the conventional art, the engaging of the teeth of the swing lever cannot be brought into snug contact with the hole of the upper base with no gap therebetween by relatively easy operation.
Therefore, an object of the present invention is to provide a seat swiveling device in a vehicle which brings the teeth or a locating lug of the swing lever into contact with the hole of the upper base or a movable base with no gap therebetween while permitting relatively easy operation for the engagement.